The present invention relates to improvements in methods and apparatuses as described in the prior related application for installing replacement pipe inside an existing underground conduit using rigid thermoplastic pipe as the replacement pipe. This application, like the prior related applications, is concerned with such installation while the thermoplastic pipe is in a collapsed, folded, heated and flexible condition.
The present invention is especially concerned with solving the problems of (1) maintaining especially large diameters and long lengths of thermoplastic pipe in a heated and flexible condition during their insertion into underground conduit, and especially such conduit that may contain standing water and other fluids that tend to cool the thermoplastic pipe during the insertion process; (2) expelling standing or flowing fluids found within an existing conduit and preventing additional fluids from flowing into the existing conduit; (3) rounding and expanding the thermoplastic pipe from its folded condition after insertion so that the new pipe fits smoothly and tightly against the interior walls of the existing conduit without trapping bubbles of air or liquids between the existing and new pipes and without causing wrinkles to form at irregularities in the existing pipe; (4) relieving the longitudinal stresses in the new plastic pipe after it has been heated and expanded against the walls of the existing conduit to prevent stress fractures, especially where holes are cut in the new pipe for connecting a lateral service pipe; (5) interconnecting a new pipe within an existing main conduit and a new pipe within an existing service conduit that intersects the main conduit; (6) quickly and thoroughly heating a spool of the folded thermoplastic pipe for insertion at a job site to render it flexible for unspooling and insertion into a conduit and maintaining the high temperature and flexibility of the pipe after it is unspooled and while it is inserted into long runs of underground conduit; and (7) repairing relatively short sections of long underground conduit remote from an access opening into the conduit.